docs: def compute_loss_curves_maps(filename, builder, rlzi, monitor):
      """
      :param filename: path to the datastore
      :param builder: LossCurvesMapsBuilder instance
      :param rlzi: realization index
      :param monitor: Monitor instance
      :returns: rlzi, (curves, maps)
      """
      with datastore.read(filename) as dstore:
          rlzs = dstore['losses_by_event']['rlzi']
          losses = dstore['losses_by_event'][rlzs == rlzi]['loss']
      return rlzi, builder.build_curves_maps(losses, rlzi)